Flotation of sulfide ores



United States Patent 3,220,551 FLOTATION OF SULFIDE ORES Samuel Payne Moyer, Spokane, Wash, assignor to American Cyauamid Company, Stamford, Conn., 21 corporation of Maine No Drawing. Filed Dec. 6, 1962, Ser. No. 242,590 7 Claims. (Cl. 209-167) This invention relates to an improvement in the process of selectively beneficiating sulfide ores, using dialkyl thiophosphoryl halides for a first rougher'separation and modifying subsequent flotation steps for selection of individual components.

The conventional methods of floating sulfide ores involve the use of two principal types of reagents, namely, the various Xanthates (ROCSSMe, where R is usually an alkyl group and Me an alkali metal, such as sodium) or the esters of dithiophosphoric acid ((RO) PSfiSH). These reagents are effective in most sulfide flotations but are not particularly effective in special cases such as acid circuits. More selective flotation is frequently desired than is available by the conventional use of such reagents. For example, when using the above-mentioned reagents, pyrite and molybdenite tend to float along with copper sulfides. If an attempt is made to first float the molybdenite (which is activated and floated with hydrocarbons) in some cases considerable pyrite and copper sulfides also float.

Newer reagents for sulfide ores which are particularly effective in floating all sulfide ores are described in United States Patent 2,621,789, Robert B. Booth and Charles L. Morris, Froth Flotation of Sulfide Minerals With Di- Alkyl Thiophosphoryl Chloride, December 16, 1952. These reagents were originally developed for use in acid circuits and very effectively float all sulfides more completely than the older reagents.

The bromine analogues are described in United States Patent 2,901,107, Arthur H. Fischer, Froth Flotation of Copper Sulfide Ores, August 25, 1959.

Both of these patents are incorporated by reference for their disclosure.

The dialkyl thiophosphoryl chlorides are less expensive than the bromine analogues, by the pound, and even lower in cost on a molar basis. In the absence of unusual cost elements, the chlorine analogue is preferred commercially, and hence its use is described in more detail below, although the same examples when repeated using the bromine analogue, give favorable results.

It has now been found that with the use of dialkyl thiophosphoryl halides a good first or rougher flotation results, and that all of the sulfide minerals tend to float. The first or rougher concentrate is then subjected to a float in a pulp with an alkaline pH, preferably using lime, which deactivates or depresses all of the minerals, hereinafter called depression. The much smaller volume of rougher concentrate is subjected to selective flotation to separate particular components.

This method can be given in flow sheet form:

Or e+water Grind with dialkyl thiophosphoryl halide Float at Natural pH Tailings discard Concentrate Raise pH, preferably with lime Second\ selective float Tailings discard Selected fractions circuits may be used. The flotation in the first rougher circuit may be run at such high loading as to be incomplete. A second flotation of the rougher tailings is made to remove the somewhat more diflicultly floatable materials. Particularly with ores containing small quantities of molybdenum, the first rougher float will contain most of the molybdenum and copper minerals and some of the pyrite. A second float with the same or a different reagent gives a second rough concentrate containing the remainder of the floatable copper and more pyrite.

One of the big costs in mineral flotation is that of grinding the ore. It is necessary that the ore be ground small enough to expose at least part of the surface of the desired mineral values to the action of the flotation reagent. With the present invention the cost of grinding can be markedly reduced. Prior to rougher flotations, a comparatively coarser grind is used which floats particles having some of the desired mineral value exposed and considerable gangue whereas the tailings contain a minimum of desired constituents. The initial grind need merely expose the mineral particles, a second grinding to finer size liberates the particles. Thus the tailings can be discarded and in the rougher flotation operation the concentrates contain nearly all of the desired values, even though the grade may be comparatively low owing to attached gangue diluent. The major weight of the ore has been thus discarded as a rougher tailing. The concentrates are reground to separate particles of value and gangue, but a much smaller weight of material is finely ground and the total grinding costs are markedly reduced.

After the fine grinding step, with the smaller weight of material to be treated more selective flotations may be used and the costs of grinding and selective treatment are markedly reduced because the early rough float eliminates the major quantity of inert materials.

Much of the theory and practice of flotation is described in a text, A. M. Gaudin, Flotation, 2nd edition, McGraw-Hill Book Company, New York, 1957. Many of the conventional steps of flotation described in this text are used with the present invention and, accordingly, the details of conventional steps are incorporated by reference from that text to avoid an unduly prolix specification.

The rougher concentrate depressed by lime or the pH shift can be selectively beneficiated by the use of various standard reagents. Some of the sulfides which normally would float with these reagents remain depressed and the other sulfides are selectively floated. This is a phenomenon which these standard reagents do not exhibit when used by themselves, since they do not become as selective unless preceded by the thiophosphoryl halide float.

A key step is that all of the mineral values in the floated concentrate can be depressed by raising the pH above 9, preferably to the region of 9-12, although a pH above 12 may be used with greater reagent consumption. The pH can be raised by the addition of any alkalizing reagent such as caustic soda or potash, soda ash, or the like, but is preferably carried out by the addition of lime as the oxide or hydroxide. The calcium ion especially seems to help in this depression and selective reactivation. Lime is usually the most economical, except where some other alkaline material is available as a by-product. The pH shift is used in conjunction with a number of other reagents. From 1 to 10 lbs. of lime per ton of original ore are used and from 0 to 2.0

" lbs. of the other depressing reagents per ton of original ore are used. The depressing reagents which are very effective include sodium sulfide, sodium ferrocyanide, calcium-cyanide, and sodium cyanide; potassium or other alkali metal sulfides, calcium sulfide and alkali and alkaline earth ferrocyanides or cyanides may be used; usually the sodium compounds are lowest in cost, although certain calcium compounds are economical to use.

When the pH has been raised above 9 all of the sulfides which have been floated are depressed. The product can then be subjected to various standard flotation techniques and reagent combinations which are known to be especially selective toward the specific mineral or minerals desired. Especially, one may use xanthates or dithiophosphates or hydrocarbons, depending on the composition of the ore to float specific minerals, one from the other. Selective beneficiation is accomplished by the proper choice of reagents. The material used and the usages vary depending on the minerals present and are standard in the art, in that promoters are used which are known to favor one specific component of a concentrate over the other components.

Unexpectedly the selectivity is far greater using such a depressed concentrate as feed than with the original ore.

Among the specific examples of such selectivity is the separation of copper sulfides by flotation from pyrite, with either xanthates or dithiophosphate esters or combinations thereof, and the separation of molybdenum sulfide by flotation from chalcopyrite and copper sulfides by the use of a hydrocarbon as flotation agent. These two examples of what can be done with the improvement in this invention illustrate very clearly the fact that the depressing and selective reactivation by proper choice of reagents varies with the specific minerals present since in the one case mentioned copper sulfides are floated and in the other case they stay depressed.

This invention can be illustrated by the following examples in which parts are by weight and based on the dry ore or other material recited, unless otherwise specified.

EXAMPLE 1 operations are summarized in the following table.

both pyrite and copper sulfides, is ground to minus mesh with 0.096 lb. per ton of ore of diethylthiophosphoryl chloride, classified, and the fines floated. The ore is conditioned with 0.067 lb. per ton of ore of a mixture of 2 parts of methylisobutylcarbinol and one part of pine oil. The resulting pulp is floated at its natural pH of 6.0 in a Fagergren flotation machine and a Rougher Concentrate No. 1 is separated. The tailings from the flotation are reconditioned with 2.07 lbs. per ton of lime, 0.117 lb. per ton of a commercial promoter consisting of a mixture of sodium mercaptobenzothiazole and sodium secondary butyl dithiophosphate, 0.120 lb. per ton of amyl xanthate, 0.27 lb. per ton of sodium sulfide and 0.009 lb. per ton of-a 2:1 mixture of methylisobutylcarbinol and pine oil. This new pulp, having a pH of 10.5, is refloated in a Fagergren flotation machine to give Rougher Concentrate No. 2 and a rougher tailing. Water from this second rougher float is separately recycled where water is short.

Rougher Concentrate No. 1 is then reground with 0.82 lb. per ton of sodium sulfide and then reconditioned with a mixture of 10.3 lbs. per ton of lime and 0.009 lb. per ton of a promoter consisting of a mixture of sodium mercaptothiazole and sodium secondary butyldithiophosphate. The resulting pulp, having a starting pH of 12.6, is then floated in a Fagergren flotation machine to give a Clean Concentrate No. 1 and Clean Tailing No. 1. Similarly, Rougher Concentrate No. 2 is reground and conditioned with 6.07 additional pounds per ton of lime. The resulting pulp, having a starting pH of 12.7, is floated in a Fagergren flotation machine to give Clean Concentrate No. 2 and Clean Tailing No. 2.

Partial oxidation of components reduces the pH to within the range of about 9 to 12. The results of these It should be noted that the present commercial beneficiation of these ores using only the standard xanthate and dithiophosphate promoters results in the recovery of a sub- A mixture of copper ores from Montana, containing 40 stantially lower amount of the total copper.

Table Assay, percent Product Percent Distribut. tion Cu Cu 11.8. Cu Fe 111501.

18. 8 6. 3 0. 14 27. 2 31. 3 85.6 5. 0 2. 0 0. 24 6. 7 78. 5 7.2 76. 2 0. 13 0. 05 1. 4 7. 2 4. 32 26. 3 0. 47 23. 1 12. 0 82. 1 14. 48 0. 34 23. 2 3. 5 0. 53 15. 7 33. 5 8. 7 6. 8 4. 47 0. 17 2. 4 0. 4 4. 25. 2 24. 1 11. 6 88. 9 Combined Tails 95. 15 0. 16 11. 1

REAGENTS USED IN POUNDS PER TON OF ORE Rod #1 #2 #1 Re- #2 Re- Reagent Mill Rgh. Rgh. grind grind Clean Clean Diethylthiophosphoryl chloride 0. 096 CaO 2. 07 10. 3 6. 07 Mixture of Sodium Mercaptobenzothiazole and Sodium sec-butyldithiophnsnharp 0. 117 0. 009 Aryl Xanthate-. 0. 120 Na s" 0 0. 27 Mixture of methylisobutylearbinol and pine oil (2:1) 0. 067 0. 009 pH- 6. 0 10. 5 l2. 6 12. 7

SCREEN ANALYSIS Classifier Overflow 1. 6 17. 2 18. 7 62. 5 Clean Gone. 1 4 1. 4 5 1. 9 95.8 Clean 00110. 2 10. 5 7. 0 8.8 7. 0 66. 7

*A.S. Cu=su1furous acid soluble copper.

A copper ore from Arizona assaying 2% copper (mostly chalcopyrite), 1% pyrite, and 0.03% molybdenite is ground to 65 mesh with 0.10 lb. of diethyl thiophosphoryl chloride per ton of ore. The resulting pulp is then conditioned in a Fagergren flotation machine with 0.06 lb. per ton of a 2:1 mixture of methylisobutylcarbinol and pine oil, and then floated to give a rougher concentrate and rougher tailing. The rougher tailing is further conditioned with 0.05 lb. of sodium di-sec-butyldithiophosphate per ton of ore and floated to give a scavenger concentrate and final tailing. Recovered water from this circuit is returned only to this circuit. The rough concentrate is conditioned with 2 lbs. of lime per ton of concentrate, and 1 lb. of sodium sulfide per ton of concentrate. It is then conditioned with 0.05 lb. of fuel oil and 0.06 lb. of methylisobutylcarbinol per ton of concentrate. The resulting pulp is then refloated to give a concentrate high in molybdenite and a tailing high in copper. This tailing is combined with the scavenger concentrate and reground with 0.05 lb., per ton of concentrate, of sodium di-sec-butyl dithiophosphate and refloated to give a clean concentrate and clean tailing. The assays of the various concentrates and tailings are as shown in the following table:

Table ASSAYS OF PRODUCTS Copper ore from Chile, which assays 1.95% copper and 0.07% M05 is'ground with 0.05 lb. per ton of diethylthiophosphoryl chloride to 65 mesh and conditioned with 0.06 lb. per ton of methylisobutylcarbinol. The resulting pulp is floated in a Fagergren flotation machine and a rough concentrate assaying 19.5% copper and 0.42% molybdenum sulfide is obtained. This rough concentrate contains 89.9% of the total copper in the ore. The rough concentrate is then reground With 0.50 lb. per ton of calcium hydroxide. The float is completely depressed and is then conditioned with 0.05 lb. per ton of kerosene. The resulting pulp is floated again to give a clean float assaying 19.9% copper and 10.3% molybdenum sulfide. The copper in this float represents 1.2% of the total copper in the ore and apparently is due to mechanical entrainment during flotation. The molybdenum in the rough concentrate represented 49.2% of the molybdenum in the ore and that in the clean concentrate represents 45.2% of the molybdenum. The tailings are combined and reground with sodium dibutylthiophosphate. The pulp is then conditioned with methylisobutylcarbonyl and refloated to give a copper concentrate and a discardable tailing. The copper concentrate contained 85.0% of the total copper available in the ore and assayed 44.69% copper. The analyses of the various concentrates and tailings are as follows:

Percent Distribution M08 Cu MOS;

Cu Cleaner Tails EXAMPLE 4 A copper ore from Chile, assaying 1.85% copper (mostly chalcopyrite) and 0.027% MoS is ground to -48 mesh with 0.02 lb. per ton of ore of diethylthiophosphoryl chloride. The resulting pulp is then conditioned in a Fagergren flotation machine with 0.06 lb. of a 1:1 mixture of methylisobutylcarbinol and pine oil per ton of ore, and then floated to give a rougher concentrate and a rougher tailing. The rougher tailing is further conditioned with 0.01 lb. of diethylthiophosphoryl chloride per ton of tailing and floated to give a scavenger concentrate and a final tailing. The rougher concentrate is conditioned with 1.3 lbs. of lime per ton of concentrate, and then further conditioned with 0.05 lb. of fuel oil and 0.06 lb. of methylisobutylcarbinol per ton of concentrate. The resulting pulp is then refloated to give a concentrate high in MoS and a tailing rich in copper. This tailing is combined with the scavenger concentrate and reground with 0.05 lb. of sodium di-sec-butyl dithiophosphate per ton of concentrate and refloated to give a clean concentrate and clean tailing. The assays of the various concentrates and tailings are as follows:

Percent Distribution Percent Assay Percent Wt.

Cale. Head Scav. Conc Molyb. Gone. 01. Gone... 01. Tail Final Tai1 I claim: 1. In the process of beneficiating sulfide ores by froth flotation which comprises effecting froth flotation at about the natural pH within the range of pH between about eral values as a froth from a tailing relatively poor in sulfide mineral values, in combination therewith the im provement which comprises: subjecting the said concentrate to a depression of all sulfide minerals by adding thereto from 1.0 to 10.0 lbs. of lime per ton of original ore solids and from 0 to 2.0 lbs. per ton of original ore solids, of a substance selected from the group consisting of an alkali metal sulfide, an alkali metal ferrocyanide, an alkali metal cyanide and calcium cyanide, at a pH between 9 and 12, and subsequently adding another promoter and subjecting said concentrate to selective flo tation of specific minerals.

2. The process of claim 1 in which the said sulfide minerals comprise mixtures of iron, molybdenum and copper sulfides.

3. A process of selectively beneficiating sulfide ore by froth flotation which comprises: grinding the ore, effecting froth flotation at about the natural pH within the range of pH between about 4.5 and 8 of the ground ore containing sulfide minerals in the presence of a promoter having the formula:

P RO 01 in which R and R are alkyl groups, separating a froth concentrate relatively rich in sulfide minerals from a froth tailing relatively poor in sulfide minerals, raising the pH of said concentrate above 9 with lime whereby the said concentrate no longer floats, subsequently adding a different promoter and subjecting said concentrate to selective flotation of specific minerals.

4. A process of selectively bneficiating sulfide ore by froth flotation which comprises: grinding the ore, efl'ecting froth flotation at about the natural pH within the range of pH between about 4.5 and 8 of a feed material containing sulfide minerals in the presence of a promoter having the formula:

RO S

P rv-o CI in which R and R are alkyl groups, separating a froth concentrate relatively rich in sulfide minerals from a froth tailing relatively poor in sulfide minerals, adding to said froth concentrate from 1.0 to 10.0 lbs. of lime per ton of original ore solids, then from 0 to. 2.0 lbs. per ton of original ore solids of a substance selected from the group consisting of an alkali metal sulfide, an alkali metal ferrocyanide, an alkali metal cyanide, and calcium cyanide, at a pH between about 9 and 12, thereby depressing sulfide minerals whereby said concentrate no longer floats, subsequently adding a different promoter and subjecting said concentrate to selective flotation of specific minerals.

5. In the process of 'beneficiating sulfide ores by froth flotation which comprises effecting froth flotation at about the natural pH within the range of pH between about 4.5 and 8 of a feed material containing sulfide minerals in the presence of a promoter having the formula:

P R'O/ \X in which R and R are alkyl groups and X is a halogen having an atomic weight between 35 and 80 followed by separation of a concentrate relatively rich in sulfide mineral values as a froth from a tailing relatively poor in sulfide mineral values, in combination therewith the improvement which comprises: reconditioning the tailings from the first flotation withlime and a mixture of sodium mercapt-obenzothiazole and sodium secondary butyl dithiophosphate and an alkyl Xanthate, and again floating,

the tailings subjecting the concentrate from the first froth flotation to regrinding and subjecting the said concentrate to a depression of all sulfide minerals by adding thereto from 1.0 to 10.0 lbs. of lime per ton of original ore solids and from 0 to 2.0 lbs. per ton of original ore solids of a substance selected from the group consisting of an alkali metal sulfide, an alkali metal ferrocyanide, an alkali a-o s R'-O Cl in which R and R are alkyl groups, separating a froth concentrate relatively rich in sulfide minerals from a froth tailing relatively poor in sulfide minerals, adding to said froth concentrate from 1.0 to 10 lbs. of lime per ton of original ore solids, then from 0 to 2.0 lbs. per ton of original ore solids of sodium sulfide at a pH between about 9 and 12, thereby depressing sulfide minerals, whereby said concentrate no longer floats, and subsequently subjecting said concentrate to selective flotation of the copper sulfides by the action of a mixture of a xanthate and a dialkyldithiophosphate.

7. A process of selectively beneficiating sulfide ores comprising a mixture of copper sulfides and molybdenum sulfides by froth flotation which comprises grinding the ore, effecting froth flotatio at about the natural pH within the range of pH between about 4.5 and 8 of a feed material containing copper sulfides and molybdenum sulfides in the presence of a promoter having the formula:

R-O S P R'o 01 in which R and R are alkyl groups, separating a froth concentrate relatively rich in sulfide minerals from a froth tailing relatively poor in sulfide minerals, adding to said froth concentrate from 1.0 to 10.0 lbs. of lime per ton or original ore solids, then from 0 to 2.0 lbs. per ton of original ore solids of sodium sulfide, at a pH between about 9 and 12, thereby depressing sulfide minerals, whereby said concentrate no longer floats, and subsequently subjecting said concentrate to selective flotation of specific minerals, including the flotation of molybdenum sulfide, using a fuel oil promoter.

References Cited by the Examiner UNITED STATES PATENTS 1,852,481 4/1932 Ruggles 209166 1,893,517 1/1933 Gaudin 209167 2,231,265 2/1941 Gaudin 209167 2,342,277 2/ 1944 Herkenhoff 209167 2,449,984 9/ 1948 Gibbs 209167 2,573,865 11/1951 Moyer 209166 2,621,789 12/ 1952 Booth 209166 2,664,199 12/1953 Barker 209167 2,811,255 10/ 1957 Nokes 209167 FOREIGN PATENTS 123,098 3/1958 Russia.

HARRY B. THORNTON, Primary Examiner.

HERBER L- MA Ex miner. 

3. A PROCESS OF SELECTIVELY BENEFICIATING SULFIDE ORE BY FROTH FLOTATION WHICH COMPRISES: GRINDING THE ORE, EFFECTING FROTH FLOTATION AT ABOUT THE NATURAL PH WITHIN THE RANGE OF PH BETWEEN ABOUT 4.5 AND 8 OF THE GROUND ORE CONTAINING SULFIDE MINERALS IN THE PRESENCE OF A PROMOTER HAVING THE FORMULA: 